Pavelsky et al. (2026) Evaluation using in-situ observations from national governments and Citizen Scientists suggests nadir altimeters can accurately measure water level changes regardless of lake area

Identification

• Journal: UNC Libraries
• Year: 2026
• Date: 2026-03-04
• Authors: Tamlin M. Pavelsky, Rajat Bhattarai, Angélica María Gómez, Sylvain Biancamaria, Shahzaib Khan, Jean-François Crétaux, Parag Vaze, Faisal Hossain, Grant Parkins, Sheikh Ghafoor, Megan Lane, Carlos Yanez, Karina Nielsen
• DOI: 10.17615/750r-em93

Research Groups

• University of North Carolina at Chapel Hill
• Université de Toulouse, Laboratoire d’Études en Géophysique et Océanographie Spatiales (LEGOS) (CNES/CNRS/IRD/UT3)
• The Technical University of Denmark
• University of Washington
• Tennessee Technological University
• Centre National d’Etudes Spatiales (CNES)

Short Summary

This study evaluates the accuracy of nadir altimeters (Sentinel-3 and Jason-3) in measuring water level changes across various lake sizes using in-situ and citizen science observations, concluding that they can accurately measure water level changes regardless of lake area.

Objective

• To evaluate the accuracy of nadir altimeters (Sentinel-3 and Jason-3) in measuring water surface elevation changes in lakes and reservoirs, particularly focusing on their effectiveness across different lake areas and identifying factors influencing accuracy.

Study Configuration

• Spatial Scale: 27 water bodies (lakes and reservoirs) for primary evaluation, combined with 61 additional lakes for factor analysis. The study specifically addresses lakes of varying sizes, including "small lakes" and those "larger than ~100 km²".
• Temporal Scale: Data from Sentinel-3 and Jason-3 nadir altimeter missions.

Methodology and Data

• Models used: Random Forest algorithm with permutation of importance.
• Data sources: In-situ observations from national governmental institutions, citizen science network (Lake Observations by Citizen Scientists and Satellites project), Sentinel-3 nadir altimeter mission, Jason-3 nadir altimeter mission.

Main Results

• A median unbiased Root Mean Square Error (ubRMSE) of 0.15 m and a Pearson correlation coefficient (R) of 0.88 were found across 27 water bodies.
• Nadir altimeters demonstrated potential to accurately estimate water surface elevation changes in small lakes.
• Water surface variability was identified as the most contributing factor to altimeter accuracy, though the order of variable importance differed based on the evaluation metric.

Contributions

• Demonstrates the potential of nadir altimeters for estimating water surface elevation changes in small lakes, expanding their known applicability beyond large lakes.
• Highlights the advantages of integrating citizen science monitoring for altimeter validation.
• Emphasizes the relevance of water surface variability as a key factor influencing altimeter accuracy.
• Introduces an implementation of a level of importance algorithm for systematically evaluating nadir altimeter validation work in literature.

Funding

• US Forest Service
• United States Geological Survey
• United States Fish and Wildlife Service
• National Aeronautics and Space Administration

Citation

@article{Pavelsky2026Evaluation,
  author = {Pavelsky, Tamlin M. and Bhattarai, Rajat and Gómez, Angélica María and Biancamaria, Sylvain and Khan, Shahzaib and Crétaux, Jean-François and Vaze, Parag and Hossain, Faisal and Parkins, Grant and Ghafoor, Sheikh and Lane, Megan and Yanez, Carlos and Nielsen, Karina},
  title = {Evaluation using in-situ observations from national governments and Citizen Scientists suggests nadir altimeters can accurately measure water level changes regardless of lake area},
  journal = {UNC Libraries},
  year = {2026},
  doi = {10.17615/750r-em93},
  url = {https://doi.org/10.17615/750r-em93}
}